Plastic containers coated on the inner surface and process for production thereof

ABSTRACT

The invention provides a plastic container with a coated inner surface having superior gas barrier properties. It further provides a plastic container with a coated inner surface capable of suppressing elution of minor components from the resin, in addition to having the superior gas barrier properties. The container has on its inner surface an amorphous carbon film formed by plasma CVD from a starting material containing carbon atoms and whose main component is carbon. In the carbon film, when the number of carbon atoms contained in the film is 100, the ratio of the number of nitrogen atoms is 15 or less, or the ratio of the number of oxygen atoms is 20 or less, or the ratio of the total number of nitrogen atoms and oxygen atoms is 27 or less. Alternatively, when the number of carbon atoms contained in the film is 100, the ratio of the number of nitrogen atoms is 15 or less, the ratio of the number of oxygen atoms is 20 or less, and the ratio of the total number of nitrogen atoms and oxygen atoms is 27 or less. The amorphous carbon film exhibits an oxygen permeability of 20×10 −5  ml/day/cm 2  or less.

TECHICAL FIELD

The present invention relates to a plastic container with a coated innersurface, having its inner surface coated with an amorphous carbon filmwhose main component is carbon, and the method for manufacturing thesame.

BACKGROUND ART

Heretofore, containers formed of various plastics such as polyethyleneterephthalate have been used as containers for holding fluid substancessuch as beverage, food, aerosol, cosmetics and medicine. Such plasticcontainers are light in weight compared to metal and glass containers,but have a drawback in that it has inferior gas barrier properties.

Recently, in order to improve gas barrier properties, there has been aproposal to coat an amorphous carbon film whose main component is carbonon the inner surface of the plastic container by plasma CVD method, andit has been put to practical use. For example, the plasma CVD methodinvolves placing the plastic container in a hollow processing chamber,evacuating the processing chamber and the interior of the plasticcontainer and maintaining vacuum, introducing a gaseous startingmaterial such as acetylene from the opening of the plastic containerinto the interior thereof, applying radiofrequency or microwave voltageso as to generate plasma in the plastic container, and forming theamorphous carbon film on the inner surface of the plastic container.

The plastic container having the amorphous carbon film coated on theinner surface thereof can exhibit superior gas barrier properties byincreasing the thickness of the film. However, if the thickness of thefilm is increased, the adhesiveness of the film to the plastic containeris deteriorated and the film cannot follow the deformation of thecontainer, so there is a drawback that the container cannot exhibitsufficient workability.

Further, if the thickness of the amorphous carbon film is increased,there is another drawback that the coloring caused by the film becomesnoticeable. The coloring caused by the film may not be preferred byconsumers, though it depends on the contents. Moreover, the coloringcaused by the film may become an obstacle to collecting and recyclingthe used plastic container such as a polyethylene terephthalate bottle.

The above problems can be overcome by reducing the thickness of theamorphous carbon film, but this solution causes the deterioration of gasbarrier properties.

The present invention aims at providing a plastic container with acoated inner surface and the method for manufacturing the same thatsolves the above-mentioned problems, by providing an amorphous carbonfilm coated on the inner surface of the container having a thin filmthickness but capable of exhibiting superior gas barrier properties.

SUMMARY OF THE INVENTION

In order to achieve the above objects, the present inventors havestudies in detail the gas barrier properties of an amorphous carbon filmto be coated on the inner surface of the plastic container. As a result,it has been discovered that the gas barrier properties of the filmdepends greatly on the ratio of atoms other than carbon contained in thefilm, especially the ratio of nitrogen atoms or oxygen atoms.

The present inventors have continued investigation based on thisdiscovery, and found that by setting the ratio of the number of nitrogenatoms or the number of oxygen atoms to the number of carbon atomscontained in the film to fall within a predetermined range, the film canexhibit superior gas barrier properties even with reduced filmthickness.

Therefore, according to the present invention, the plastic containerwith a coated inner surface has an amorphous carbon film formed byplasma CVD from a starting material containing carbon atoms andcontaining carbon as a main component on the inner surface, wherein theamorphous carbon film characterizes in that when the number of carbonatoms contained in the film is 100, one of the following is fulfilled: aratio of a number of nitrogen atoms to the number of carbon atoms is 15or less; a ratio of a number of oxygen atoms to the number of carbonatoms is 20 or less; a ratio of a total number of nitrogen atoms andoxygen atoms to the number of carbon atoms is 27 or less; or the ratioof the number of nitrogen atoms to the number of carbon atoms is 15 orless, the ratio of the number of oxygen atoms to the number of carbonatoms is 20 or less, and the ratio of the total number of nitrogen atomsand oxygen atoms to the number of carbon atoms is 27 or less.

According to the plastic container with a coated inner surface of thepresent invention, the gas barrier properties of the film can beenhanced by having the ratio of the number of nitrogen atoms or oxygenatoms to the number of carbon atoms contained in the amorphous carbonfilm fall within the above range. Therefore, according to the presentplastic container with a coated inner surface, superior gas barrierproperties can be achieved even when the thickness of the amorphouscarbon film is reduced.

Moreover, since the amorphous carbon film is thin, it has goodadhesiveness to the container, and can follow the deformation of thecontainer being subjected to a deformation process. Accordingly, theplastic container with a coated inner surface of the present inventionhas excellent workability since the gas barrier properties thereof willnot deteriorate through deformation.

Furthermore, the amorphous carbon film has reduced film thickness andlittle coloring. Accordingly, the plastic container with a coated innersurface of the present invention prevents consumers from avoiding thecontainer regardless of its content, and provides no obstacle tocollecting and recycling the used container.

On the other hand, if the ratio of the number of nitrogen atoms oroxygen atoms to the number of carbon atoms contained in the amorphouscarbon film exceeds the above range, the oxygen permeability or carbonicacid gas permeability of the film increases, and the container can nolonger exhibit sufficient gas barrier properties. As a result, if suchcontainer is filled with beverage or other contents and left in roomtemperature or in a hot-warmer, the practical shelf life becomes shortand thus not preferable.

The ratio of the number of nitrogen atoms or oxygen atoms to the numberof carbon atoms contained in the amorphous carbon film can be measuredby using an electron spectroscopy device for chemical analysis (ESCA).

There is another drawback with respect to the plastic container, inwhich very small amounts of minor components such as oligomers, lowmolecular-weight components and polymerization catalysts residing in theresin elute into the contents and affect the flavor etc. of thebeverages or foods. Thus, there is a demand for a technique capable ofimproving the gas barrier properties and simultaneously preventingelution of minor components.

According to the studies performed by the present inventors, theamorphous carbon film containing carbon as its main component issuperior in both the gas barrier properties and the function to suppresselution of minor components if the oxygen permeability is as low aspossible.

Therefore, the plastic container with a coated inner surface accordingto the present invention characterizes in that the amorphous carbon filmhas an oxygen permeability of 20×10⁻⁵ ml/day/cm² or less.

According to the present plastic container with a coated inner surface,the permeability of the amorphous carbon film is 20×10⁻⁵ ml/day/cm² orless, by which the film can be reduced of thickness while exhibitingadvantageous gas barrier properties and suppressing elution of minorcomponents into the content. Therefore, the plastic container with acoated inner surface according to the present invention achievessuperior adhesiveness and superior workability between the amorphouscarbon film and container, so that the film will not detach from thecontainer even when the container deforms or receives impact.

Moreover, since the amorphous carbon film is thin and has smallcoloring, the present plastic container with a coated inner surface willnot be avoided by the consumers regardless of its contents, and will notcause any obstruction when collecting and recycling the used container.

The oxygen permeability of the plastic container with a coated innersurface can be measured using a gas transmission rate measuring devicesuch as an OX-TRAN (trade name) manufactured by MOCON, and based on JISK 7126. Further, the oxygen permeability of the amorphous carbon filmitself can be computed based on the measurement of the oxygenpermeability of the plastic container thus measured and the oxygenpermeability of a plastic container having no film coated thereon.

According to the present plastic container with a coated inner surface,it is preferable that the amorphous carbon film has a thickness in therange of 0.007 through 0.08 μm (70 through 800 angstrom). If thethickness of the amorphous carbon film is less than 0.007 μm, thecoloring by the film is suppressed but the oxygen permeability thereofincreases. Further, if the thickness of the amorphous carbon filmexceeds 0.08 μm, the oxygen permeability is reduced but the coloringincreases, deteriorating recycling efficiency and reducing adhesivenessand workability of the film with respect to the container.

According to the present plastic container with a coated inner surface,the plastic container is formed of a polyester resin, and if it has abody portion having a thickness in the range of 0.2 through 0.5 mm, theamorphous carbon film having the above range of oxygen permeability willexert superior gas barrier properties and will have an effect tosuppress elution of minor components.

Furthermore, according to the present plastic container with a coatedinner surface, the plastic container preferably has an inner volume of2000 ml or less, in order to form the amorphous carbon film having theabove range of oxygen permeability.

The plastic container with a coated inner surface according to thepresent invention is manufactured by placing the plastic container in aplasma CVD apparatus, maintaining the interior of the plasma CVDapparatus to a predetermined vacuum degree, feeding a gaseous startingmaterial including carbon atoms into the plastic container, supplying apredetermined energy into the plasma CVD apparatus to generate plasmainside the plastic container to thereby form an amorphous carbon filmcontaining carbon as the main component on the inner surface of theplastic container.

However, according to the above method, the ratio of the number ofnitrogen atoms or oxygen atoms to the number of carbon atoms containedin the amorphous carbon film being formed exceeds the above-mentionedrange, and thus the film cannot exert sufficient gas barrier properties.

The possible causes of the nitrogen atoms or oxygen atoms contained inthe amorphous carbon film include a case where removal of air isinsufficient when the plasma CVD apparatus is set to predeterminedvacuum degree, a case where airtightness of the plasma CVD apparatus isinsufficient and air leak occurs, a case where nitrogen gas is used asthe carrier gas of the gaseous starting material and the startingmaterial further includes nitrogen-containing or oxygen-containingcompounds such as dimethylformamide whose concentration becomes high, ora case where nitrogen-containing or oxygen-containing components areabsorbed to the inner surface of the plastic container.

Moreover, if the removal of air is insufficient during reduction ofpressure of the interior of the plastic container placed in the plasmaCVD apparatus to a determined vacuum degree, air will mix into the gascomponents including the starting material fed into the plasticcontainer. In such case, since air contains nitrogen and oxygen, theformed film tends to have deteriorated gas barrier properties due to theexistence of oxygen compared to the case where only nitrogen is mixedinto the gas components.

Therefore, according to the present invention, the plastic containerwith a coated inner surface can be manufactured advantageously if thegas components including the starting material fed into the plasticcontainer contains a nitrogen gas whose amount being mixed to the totalamount of the gas components is 20% by volume or less, preferably 15% byvolume or less; or an oxygen gas whose amount being mixed to the totalamount of the gas components is 10% by volume or less, preferably 7% byvolume or less; or an oxygen gas whose amount being mixed to the totalamount of the gas components is 10% by volume or less, and the totalamount of nitrogen gas and oxygen gas being mixed is 15% by volume orless, preferably 10% by volume or less.

According to the present manufacturing method, the ratio of the numberof nitrogen atoms or oxygen atoms to the number of carton atomscontained in the amorphous carbon film can be suppressed to fall withinthe above-mentioned range by controlling the amount of nitrogen gas oroxygen gas contained in the gas components fed to the plastic containerto the above-mentioned range. However, in doing so, once themanufacturing process is started, it is difficult to detect and controlthe change in the amount of nitrogen-containing compounds or air mixinginto the starting material and exceeding the above-mentioned range. As aresult, the ratio of the number of nitrogen atoms or oxygen atoms to thenumber of carbon atoms contained in the amorphous carbon film cannot besuppressed to fall within the predetermined range, and thus it may notbe possible to obtain a plastic container having the predetermined gasbarrier properties.

Therefore, according to the present manufacturing method, it ispreferable to detect an emission intensity of plasma of nitrogen basedon an emission spectrum of the plasma generated by the gas componentscontaining the starting material being fed into the plastic container,and controlling a concentration of a nitrogen containing compound or anamount of air being mixed into the gas components.

According to the present manufacturing method, gas components containingthe starting material are fed into the plastic container and apredetermined amount of energy is supplied into the plasma CVDapparatus, to thereby generate plasma in the plastic container.Thereafter, the emission spectrum of the plasma is measured to therebydetect the emission intensity of the plasma of the nitrogen component(hereinafter referred to as nitrogen plasma emission intensity). Thus,it is possible to determine based on the nitrogen plasma emissionintensity the existence of nitrogen in the gas components and the amountthereof. If the nitrogen plasma emission intensity exceeds apredetermined intensity, it is determined that the nitrogen componentcontained in the gas components exceeds a predetermined range, and thecause thereof is to be eliminated.

According to the present manufacturing method, the cause is actuallyeliminated by controlling the concentration of the nitrogen-containingcompound or the amount of air being mixed into the gas components fed tothe plastic container. As a result, the nitrogen component contained inthe gas components can be suppressed to within a predetermined range.

Thus, according to the present manufacturing method, it is possible toprevent plastic containers having deteriorated gas barrier propertiesfrom being manufactured when the amount of air or nitrogen-containingcompound being mixed into the gas components fed to the plasticcontainer exceeds the predetermined range. As a result, according to thepresent manufacturing method, process management and quality managementcan be performed easily, and the yield factor of the product can beimproved.

The concentration of the nitrogen-containing compound or the amount ofair being mixed into the gas components can be controlled throughfeedback control, for example, and when a nitrogen plasma emissionintensity exceeding the predetermined value is detected, a procedure forsuppressing the amount of nitrogen-containing compound being mixed in iscarried out so as to assure that the plastic containers to bemanufactured subsequently exhibit the predetermined gas barrierproperties. However, according to the aforementioned feedback control,the predetermined gas barrier properties cannot be obtained for theplastic container being manufactured at the time the nitrogen plasmaemission intensity exceeding the predetermined range was detected.

Therefore, according to the present manufacturing method, when theemission intensity of plasma of nitrogen exceeds a predeterminedintensity, the plastic container having the amorphous carbon film coatedthereon is eliminated from the manufacturing process. When this processis performed, the plastic container having been manufactured at the timethe nitrogen plasma emission intensity exceeded the predetermined rangewill be removed from the manufacturing process subsequent to forming thefilm, and thus it becomes possible to prevent plastic containers havingdeteriorated gas barrier properties from being mixed with the goodcontainers.

According to the present manufacturing method, the nitrogen plasmaemission intensity is detected by selectively detecting the emission ofa specific wavelength range in the emission spectrum. The amount ofnitrogen components contained in the gas components can be computed bypreparing in advance a calibration curve regarding the amount ofnitrogen component and the intensity of emission of a specificwavelength range, and by comparing the detected nitrogen plasma emissionintensity with the calibration curve.

The resins for forming the plastic container with a coated inner surfacecan include polyester resins such as polyethylene terephthalate,polyolefin resins such as polyethylene and polypropylene, polyamideresins, polyether resins and acrylic resins, which are publicly known.However, if the plastic container with a coated inner surface serves asa beverage bottle, the resin should preferably be polyester resin orpolyolefin resin.

According to the amorphous carbon film formed by the presentmanufacturing method, it is preferable that the film has a thickness inthe range of 0.02 through 0.08 μm (200 through 800 angstrom) when theoxygen permeability related to suppressing elution of minor componentsfrom the plastic container is not considered. If the thickness of thefilm is less than 0.02 μm, the coloring by the film can be suppressed,but the gas barrier properties thereof is deteriorated regardless of thecomponents of the film, and thus cannot exert sufficient content keepingquality. Further, if the thickness of the film exceeds 0.08 μm, the gasbarrier properties are enhanced, but the coloring becomes deeperdeteriorating the recycling efficiency and reducing the adhesiveness andworkability of the film with respect to the plastic container.

The coloring by the amorphous carbon film can be represented by a Δb*value computed as a difference between b* values determined bytransmitting light perpendicularly with respect to the side wall of theplastic container by a color-difference meter before and after formingthe film and comparing them. The b* value is a value indicating thecolor saturation in the yellow direction in a L*a*b* color specificationsystem (JIS Z 8729) standardized by the International Commission onIllumination (CIE), and in general, the value of Δb* increases as thethickness of the amorphous carbon film increases.

Furthermore, the starting material to be used according to the presentmanufacturing method can include unsaturated hydrocarbon compounds suchas acetylene, ethylene and propylene, saturated hydrocarbon compoundssuch as methane, ethane and propane, and aromatic hydrocarbon compoundssuch as benzene, toluene and xylene. The above-listed compounds can beused by itself as the starting material or by mixing two or morecompounds, but in order to form a film as a polymeric thin film, it ispreferable to use the unsaturated hydrocarbon compound such as acetyleneor ethylene by itself.

Therefore, according to the present manufacturing method, the startingmaterial should preferably be substantially composed of acetylene. Thestarting material substantially composed of acetylene can includeunavoidable impurities other than acetylene. Furthermore, according tothe present manufacturing method, the starting material can include 60%by volume or more, preferably 80% by volume or more of acetylene to thewhole starting material. The starting material can contain as othercomponents film modifying agents such as hydrogen, organosiliconcompounds and film-forming organic compounds. Further, the startingmaterial can be diluted by rare gases such as argon or helium.

The present manufacturing method preferably comprises the steps ofmaintaining the interior of the plastic container placed in the plasmaCVD apparatus to a vacuum degree of 1 through 50 Pa, feeding the gaseousstarting material containing the carbon atoms into the plastic containerwithin the range of 0.1 through 0.8 sccm/cm² with respect to an innersurface area of the plastic container, radiating microwaves with energywithin the range of 150 through 600 W into the plasma CVD apparatus, andgenerating plasma in the plastic container during a period of timewithin the range of 0.2 through 2.0 seconds, thereby forming theamorphous carbon film on the inner surface of the plastic container.

According to the present manufacturing method, the amorphous carbon filmcan be formed on the inner surface of the plastic container by placingthe plastic container in the plasma CVD apparatus that utilizesmicrowaves, maintaining the interior of the plasma CVD apparatus to avacuum degree in the above-mentioned range, feeding the gaseous startingmaterial into the plastic container, and radiating microwaves into theplasma CVD apparatus.

According to the plasma CVD apparatus, in the process of generatingplasma from the gaseous starting material and forming the amorphouscarbon film, it is necessary to set the interior of the plasticcontainer to a vacuum degree within the range of 1 through 50 Pa,preferably 2 through 30 Pa. If the vacuum degree is less than 1 Pa, ittakes too much time to form the film. If the vacuum degree exceeds 50Pa, the adhesiveness and workability of the formed film with respect tothe plastic container is deteriorated.

Next, the feeding amount of the starting material should preferably bewithin the range of 0.1 to 0.8 sccm/cm² to the surface area of thecontainer. If the feeding amount of the starting material is less than0.1 sccm/cm², the generation of plasma becomes difficult, the thicknessof the amorphous carbon film is reduced and the gas barrier propertythereof is deteriorated. On the other hand, if it exceeds 0.8 sccm/cm²,the thickness of the film becomes too thick and coloring by the filmbecomes noticeable.

Moreover, the radiation time of the microwaves should preferably fallwithin the range of 0.2 through 2.0 seconds. If the radiation time ofmicrowaves is less than 0.2 seconds, the generation of plasma becomesdifficult and the thickness of the amorphous carbon film is reduced. Onthe other hand, if the time exceeds 2.0 seconds, the film becomes toothick and coloring by the film becomes noticeable, thus it is notdesirable.

Further, by controlling the feeding amount of starting material andradiation time of microwaves to fall within the above-mentioned rangeand by adjusting the energy of the microwaves to fall within the rangeof 150 through 600 W, it is possible to obtain a plastic container witha film having a thickness of 0.02 through 0.08 μm, the Δb* value withinthe range of 2 through 7, and having superior gas barrier properties.

The energy of the microwaves relates closely with the film structure,the coloring and the gas barrier property, and if the energy is lessthan 150 W, the ratio of sp² bonds forming a conjugated double bondbetween the carbon-carbon of the amorphous carbon film increases. As aresult, a film having reduced gas barrier properties is formed, andcoloring by the film becomes deeper.

Moreover, when the energy of the microwaves exceeds 600 W, the ratio ofsp³ bonds forming a single bond of a tetrahedron arrangement between thecarbon-carbon of the film increases. As a result, the coloring by thefilm becomes less noticeable, but the gas barrier property thereof isdeteriorated.

The plastic container with the coated inner surface can be a rigidcontainer having self-shape holding property, such as a polyethyleneterephthalate container, or can be a container having no self-shapeholding property, such as a container formed of soft polyethylene.Examples of a container having no self-shape holding property caninclude a soft polyethylene container for storing fluid such astransfusion in the field of medicine, and a container storing pure wateror drinking water of 0.5 to 20 liter and having its exterior supportedby a container board or the like.

According to the present manufacturing method, if the plastic containerwith the coated inner surface is a container having no self-shapeholding property, the interior of the container placed in the plasma CVDapparatus is maintained at high-pressure than the exterior thereof.Thereby, it is possible to provide a self-shape holding property to theplastic container, so as to form an amorphous carbon film on the innersurface of the container.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory cross-sectional view illustrating one exampleof an apparatus for manufacturing a plastic container according to thepresent invention.

FIG. 2 is an explanatory cross-sectional view illustrating anotherexample of an apparatus for manufacturing a plastic container accordingto the present invention.

FIG. 3 is a graph showing one example of spectrum of plasma generatedwhen the gas components fed into the plastic container are only gaseousstarting materials.

FIG. 4 is a graph showing one example of spectrum of plasma generatedwhen the gas components fed into the plastic container contain nitrogencomponent in addition to the gaseous starting materials.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the preferred embodiments of the burner according to the presentinvention will be explained with reference to the accompanying drawings.

First, a plastic container with a coated inner surface according to afirst preferred embodiment of the present invention is a 350 mlpolyethylene terephthalate bottle (hereinafter abbreviated as PETbottle) for beverages such as green tea drinks, carbonated drinks, beeretc., and has an amorphous carbon film coated on its inner surface. Theamorphous carbon film formed on the PET bottle characterizes in thatwhen the number of carbon atoms contained in the film is 100, the ratioof the number of nitrogen atoms to the number of carbon atoms is 15 orless, or the ratio of the number of oxygen atoms to the number of carbonatoms is 20 or less, or the ratio of the total number of nitrogen atomsand oxygen atoms to the number of carbon atoms is 27 or less.

Further, the amorphous carbon film can be characterized in that when thecarbon atoms contained in the film is 100, the ratio of the number ofnitrogen atoms to the number of carbon atoms is 15 or less, the ratio ofthe number of oxygen atoms to the number of carbon atoms is 20 or less,and the ratio of the total number of nitrogen atoms and oxygen atoms tothe number of carbon atoms is 27 or less.

The amorphous carbon film has a thickness within a range of 0.02 to 0.08μm (200 to 800 angstrom), for example.

The PET bottle according to the present embodiment can be manufacturedusing a plasma CVD apparatus illustrated in FIG. 1, for example.

In FIG. 1, a plasma CVD apparatus 1 comprises a processing chamber 4defined by a side wall 2 formed of Pyrex (registered trademark) glassand a bottom plate 3 movable in the vertical direction, and a microwavegenerating unit 5 disposed at a position confronting the side wall 2. Anevacuation chamber 8 defined by a side wall 6 and an upper wall 7 isequipped to the area above the processing chamber 4, and a partitionwall 9 is provided between the processing chamber 4.

The bottom plate 3 allows a PET bottle 10 to be placed thereon andelevates, thereby storing the PET bottle 10 in the processing chamber 4.The PET bottle 10 stored in this manner is placed so that the interiorof the container communicates with an evacuation hole 12 formed to thepartition wall 9 via an opening portion supporter 11. The openingportion supporter 11 has an upper projection 13 inserted airtightly tothe evacuation hole 12, and an opening supporting unit 14 inserted tothe opening of the PET bottle 10. There is a gap between the openingsupporting unit 14 and the inner surface of the opening of the PETbottle 10 so as to allow the opening supporting unit 14 to be insertedto or removed from the opening, but the inner surface of the opening ofthe PET bottle 10 is substantially masked by the opening supporting unit14, so that an amorphous carbon film mentioned in detail later will notbe formed on the inner surface of the opening.

The processing chamber 4 and the evacuation chamber 8 are communicatedvia an air hole 15 with a valve 16 disposed on the partition wall 9, andan opening 17 formed to the side wall 6 of the evacuation chamber 8 isconnected to a vacuum equipment not shown. The upper wall 7 of theevacuation chamber 8 supports via a seal 18 a gas inlet tube 19 forfeeding a gaseous starting material (hereinafter referred to as materialgas), and the gas inlet tube 19 is passed through the upper wall 7 andthe opening portion supporter 11 to be inserted to the PET bottle 10.Further, a gap is formed between the gas inlet tube 19 and the innercircumference wall of the opening portion supporter 11 enabling air tobe evacuated from or supplied to the interior of the PET bottle 10.

When manufacturing a PET bottle according to the present embodimentusing the plasma CVD apparatus 1 shown in FIG. 1, at first, the bottomplate 3 on which the PET bottle 10 is placed is elevated, storing thePET bottle 10 in the processing chamber 4. Next, the interior of theevacuation chamber 7 is evacuated by the operation of a vacuum equipmentnot shown, by which the interior of the processing chamber 4 isdecompressed via the air hole 15. Simultaneously, the interior of thePET bottle 10 is decompressed to a vacuum degree within the range of 1to 50 Pa via the gap between the gas inlet tube 19 inserted to theevacuation hole 12 and the inner circumference surface of the openingportion supporter 11.

Next, material gas is fed into the PET bottle 10 through the gas inlettube 19. In the plasma CVD apparatus 1, material gas is continuously fedwhile performing evacuation continuously through the vacuum equipment tothereby maintain the interior of the processing chamber 4 and the PETbottle 10 to the above-mentioned vacuum degree. Moreover, the amount ofmaterial gas to be fed is set to an appropriate amount corresponding tothe surface area of the object PET bottle 10 and the thickness of thefilm to be formed. The amount of material gas to be fed shouldappropriately be within the range of 0.1 to 0.8 sccm/cm² per containersurface area in order to form a film with a thickness of 0.02 to 0.08 μmto a PET bottle 10 with an inner volume within the range of 200 to 2000ml.

The material gas can be any of the following: aliphatic unsaturatedhydrocarbons such as acetylene and ethylene; aliphatic saturatedhydrocarbons such as methane, ethane and propane; aromatic hydrocarbonssuch as benzene, toluene and xylene; and other carbon-containingcompounds. The material gas can be used alone or in a mixture containingtwo or more gases, and can additionally contain as a film reformingagent a small amount of hydrogen, organosilicon compounds or otherorganic compounds having film forming properties. The material gas canalso be diluted with inert gas such as argon and helium.

However, in order to form a polymeric amorphous carbon thin film havingexcellent gas barrier properties in a shorter time, it is substantiallysuitable to use acetylene as the material gas, and it is preferable thatthe material gas contain 60% by volume or more acetylene, and morepreferably, contain 80% by volume or more acetylene. If the material gasis substantially formed of acetylene, the acetylene can containimpurities that are unavoidably mixed therein during manufacturingprocesses and the like.

The material gas is formed so that the amount of nitrogen gas beingmixed to the total amount of material gas is 20% by volume or less,preferably 15% by volume or less, or the amount of oxygen gas mixed tothe total amount of gas is 10% by volume or less, preferably 7% byvolume or less. Alternatively, the material gas can be formed so thatthe amount of oxygen gas being mixed to the total amount of material gasis 10% or less, and at the same time, the total amount of nitrogen gasand oxygen gas being mixed is 15% by volume or less, preferably 10% byvolume or less.

While the material gas is being fed, the microwave generating unit 5 isoperated to irradiate microwaves of 2.45 GHz and 150 to 600 W for 0.2 to2.0 seconds, preferably 0.4 to 1.5 seconds, so as to electromagneticallyexcite the material gas to generate plasma within the PET bottle 10 andto form an amorphous carbon film (not shown) on the inner surface of thePET bottle. At this time, as mentioned earlier, material gas iscontinuously fed while performing evacuation through the vacuumequipment to maintain the interior of the processing chamber 4 and thePET bottle 10 to the predetermined vacuum degree, so as to form a stablefilm. Moreover, if the irradiation time of the microwaves is less than0.2 seconds, the film may not have the desired thickness, and if itexceeds 2.0 seconds, the film thickness may become excessive andcoloring may become deeper.

Next, when the feeding of material gas is terminated, the microwavegenerating unit 5 is stopped, the interior of the processing chamber 4and the PET bottle 10 is returned to atmospheric pressure, the bottomplate 3 is lowered and the PET bottle 10 is taken out, by which theprocess is completed. The microwave generating unit 5 can either bestopped simultaneously when the feeding of the material gas isterminated, but it can be operated in extension for a short time. Bythis operation, the material gas components residing in the containercan be deposited completely as film, according to which the gas barrierproperties of the formed PET bottle and the flavor resistance propertieswhen the bottle 10 is filled with contents can be further enhanced.

Incidentally, when the PET bottle according to the present embodiment ismanufactured as described in the apparatus shown in FIG. 1, once themanufacturing is started, the amount of nitrogen-containing compounds orair being mixed into the material gas may vary and exceed thepredetermined range, but it is difficult to detect and control the same.Therefore, the PET bottle according to the present embodiment can bemanufactured using a plasma CVD apparatus 1 illustrated in FIG. 2.

The plasma CVD apparatus 1 shown in FIG. 2 comprises, in addition to thecomponents of the plasma CVD apparatus 1 shown in FIG. 1, a lightreceive unit 20 for receiving the emission of light accompanying thegeneration of plasma in the plastic container 10. The light receive unit20 is connected to a plasma emission spectrometry device 22 via anoptical fiber 21. The plasma emission spectrometry device 22 is equippedwith a band-pass filter 23, a detecting means 24 and a control means 25,and the optical fiber 21 is connected to the band-pass filter 23. Themain control means 25 is connected to a gas component control means 26for controlling the concentration of nitrogen-containing compound or theamount of air mixed into the material gas, and a defective containereliminating means 27 for eliminating the containers 10 that are notequipped with predetermined gas barrier properties as defectivecontainers from the manufacturing process.

The plasma CVD apparatus 1 shown in FIG. 2 is capable of manufacturingthe PET bottle according to the present embodiment in the same manner asthe plasma CVD apparatus 1 shown in FIG. 1, but when the microwavegenerating unit 5 is operated to cause plasma to be generated by the gascomponents fed into the plastic container 10, the apparatus detects theplasma emission intensity of nitrogen included in the plasma emissionspectrum.

The nitrogen plasma emission intensity is detected by analyzing theemission spectrum in the plasma emission spectrometry device 22.According to the plasma emission spectrometry device 22, the emission ofplasma generated in the plastic container 10 is received by the lightreceive unit 20 and sent via the optical fiber 21 to the band-passfilter 23.

At this time, if the gas components fed into the plastic container 10contains only material gas, the emission spectrum of plasma will be asshown in FIG. 3. On the other hand, if the gas components fed into theplastic container 10 contain nitrogen components in addition to thematerial gas, the emission spectrum will be as shown in FIG. 4.According to the spectrum shown in FIG. 4, the radiation within thewavelength region of 700 to 800 nm corresponds to the emission specificto nitrogen plasma, which is considered to be in the region that isrelatively hard to overlap with the emission of other components.

Thus, the band-pass filter 23 selectively transmits the radiation in theabove-mentioned wavelength region of 700 to 800 nm, and the intensity ofthe radiation of this wavelength region is detected by the detectingmeans 24 as the nitrogen plasma emission intensity. Next, the data onthe nitrogen plasma emission intensity detected by the detecting means24 is sent to the main control means 25. The main control means 25stores in its memory a calibration curve created in advance regardingthe amount of nitrogen components contained in the gas components andthe intensity of radiation in the above wavelength region, and bycomparing the data on the nitrogen plasma emission intensity with thecalibration curve, the amount of nitrogen components contained in thegas components can be computed.

When the amount of nitrogen components is detected to exceed 20% byvolume of the total amount of gas components, the main control means 25adjusts the concentration of nitrogen-containing compound to be mixedinto the gas components via the gas component control means 26, therebycontrolling the gas components fed into the plastic container 10 tocontain 20% by volume or less of nitrogen gas to the total amount of gascomponents. Alternatively, the amount of air being mixed into the gascomponents can be adjusted so that the gas components fed into theplastic container 10 contains 10% by volume or less of oxygen gas to thetotal amount of gas components and contains 15% by volume or less of atotal of the nitrogen gas and oxygen gas.

As a result, the subsequent plastic container 10 can have the amount ofnitrogen and oxygen contained in the formed film to be controlled withinthe determined range, and thus it is possible to prevent manufacture ofa plastic container 10 with deteriorated gas barrier properties.

Further, when the amount of nitrogen components is detected to exceed20% by volume of the total amount of gas components, the main controlmeans 25 eliminates the plastic container 10 taken out of the processingchamber 4 as defective container from the manufacturing processes viathe defective container eliminating means 27.

According to the present embodiment, the plasma emission generated inthe plastic container 10 is received by the light receive unit 20 andanalyzed by the plasma emission spectrometry device 22 equipped with aband-path filter 23, a detecting means 24 and a control means 25, but itis also possible to analyze the same without using the band-path filter23. Moreover, instead of the light receive unit 20, an optical sensorcan be disposed to the position confronting the side wall 2 to analyzethe emission.

According further to the present embodiment, the film is coated on theinner surface of the PET bottle for beverages. However, the plasticcontainer of the present invention is not limited to PET bottles forbeverages, and can be a container formed of various plastics such aspolyester resins, polyolefin resins, polyamide resins, polyether resinsor acrylic resins. The above-mentioned resins have various propertiescorresponding to their molecular structures, but for various uses inwhich gas barrier properties are required, the present invention can beapplied regardless of the type of resins. As for the contents, they arenot limited to green tea beverage, carbonated beverage and beer, but canbe other beverages such as tea other than green tea, coffee andsparkling liquor, foods such as sauce and soy sauce, or fluid substancessuch as aerosol, cosmetics and medicine.

Moreover, when the plastic container is formed of a soft rein such as asoft polyethylene resin, the container may have no self-shape holdingproperty in which the container lacks the ability to hold its shape. Inthis case, when the container is stored in the processing chamber 4 ofthe plasma CVD apparatus 1 shown in FIG. 1 and the interior of thechamber 4 and the container is decompressed, the exterior of thecontainer can be maintained at higher vacuum than the interior of thecontainer so as to maintain the container shape and to form the film onthe inner surface of the container.

Next, the plastic container with a coated inner surface according to asecond embodiment of the present invention can be formed for example byblow molding polyester resin, comprising a body portion having athickness within the range of 0.2 to 0.5 mm and an inner volume of 2000ml or less. The polyester resin is a resin obtained through condensationpolymerization reaction of polyalcohol and polycarboxylic acid compound,through transesterification or the like, and the examples of which caninclude polyethylene terephthalate resin, polybutylene terephthalate andpolyethylenenaphthalate. The plastic container with a coated innersurface according to the present embodiment is used for example as acontainer for beverages such as tea, coffee, sports drink, carbonatedbeverage, sparkling liquor and beer, container for food such as sauceand soy sauce, an aerosol container or the like.

The plastic container with a coated inner surface according to thepresent invention is, for example, a PET bottle comprising a bodyportion with a thickness within the range of 0.2 to 0.5 mm and an innervolume of 350 ml. The PET bottle has on its inner side an amorphouscarbon film containing carbon as its main component, and the film has anoxygen permeability of 20×10⁻⁵ ml/day/cm². The PET bottle can besubjected to required treatments, such as heat resistance treatment orthe like.

The amorphous carbon film can contain nitrogen, oxygen etc., and in suchcase, when the number of carbon atoms contained in the film is 100, theratio of the number of nitrogen atoms to the number of carbon atoms is15 or less, or the ratio of the number of oxygen atoms to the number ofcarbon atoms is 20 or less, or the ratio of the total number of nitrogenatoms and oxygen atoms to the number of carbon atoms is 27 or less.Alternatively according to the present amorphous carbon film, when thenumber of carbon atoms contained in the film is 100, the ratio of thenumber of nitrogen atoms to the number of carbon atoms is 15 or less,the ratio of the number of oxygen atoms to the number of carbon atoms is20 or less, and the ratio of the total number of nitrogen atoms andoxygen atoms to the number of carbon atoms is 27 or less.

If the ratio of the number of nitrogen atoms or the number of oxygenatoms to the number of carbon atoms in the film falls within the aboverange, the amorphous carbon film has a thickness within the range of0.007 to 0.08 μm (70 to 800 angstrom), for example. However, if theamorphous carbon film has an oxygen permeability falling within theabove range, the thickness thereof can be less than 0.007 μm (70angstrom).

The PET container can be manufactured by a plasma CVD apparatus 1illustrated in FIG. 1 or FIG. 2.

The PET bottle 10 according to the present embodiment has superior gasbarrier properties because of the amorphous carbon film, andsimultaneously, prevents the elution of minor components such asoligomer, low molecular-weight component, polymerization catalyst or thelike contained in the resin forming the PET bottle 10. Since littlecoloring is caused by the amorphous carbon film to the PET bottle 10,the consumers will not avoid the bottle, and the used PET bottle 10 canbe recycled without any obstruction.

The present embodiment described an example of a case in which theamorphous carbon film was coated on the inner surface of a PET bottle10. However, the plastic container according to the present embodimentis not limited to PET bottles, and the container can be formed of otherpolyester based resins, such as polybutylene terephthalate,polyethylenenaphthalate and soon. At this time, if necessary, thepolyester based resins can be mixed with other resins such as allylresin, phenol resin, polyether resin, epoxy resin, acrylic resin,ethylene copolymerization resin and so on, and the resins can contain anultraviolet absorber, an ultraviolet screening agent, an antioxidant andso on.

Furthermore, the plastic container according to the present embodimentcan be formed of various plastics other than polyester based resins,such as polyolefin based resins, polyamide based resins, polyether basedresins, polyacrylic resins and so on.

According to the above-mentioned embodiments, a plasma CVD apparatususing microwaves as means for electromagnetically exciting the materialgas was described as an example, but it is also possible to use anapparatus to electromagnetically excite the material gas by applying RFvoltage between electrodes arranged on the inner and outer surfaces ofthe PET bottle 10. However, in order to form an amorphous carbon filmhaving good adhesiveness, workability and superior gas barrierproperties, it is appropriate to adopt the plasma CVD apparatus usingmicrowaves.

Next, we will describe the examples and comparative examples.

EXAMPLE 1

The present example used the plasma CVD apparatus 1 illustrated in FIG.1 to manufacture a 350 ml PET bottle having its inner surface coatedwith amorphous carbon film.

At first, according to the present example, the PET bottle 10 was storedin the processing chamber 4 of the plasma CVD apparatus 1 illustrated inFIG. 1, and the processing chamber 4 was decompressed to reduce thepressure inside the PET bottle 10 to a vacuum degree of 10 Pa. Next, amaterial gas composed of acetylene gas was fed into the PET bottle 10 ata flow rate of 0.4 sccm/cm² with respect to the inner surface area ofthe PET bottle 10, and microwaves of 2.45 GHz and 380 W was radiated for0.6 seconds while maintaining the interior of the PET bottle 10 to thevacuum degree of 10 Pa.

As a result, a PET bottle 10 having an amorphous carbon film with athickness of 0.04 μm (400 angstrom) coated on the inner surface wasobtained.

Next, the PET bottle 10 obtained according to the present example wassubjected to measurement in an apparatus for electron spectroscopy forchemical analysis (ESCA) to detect the ratio of the number of nitrogenatoms or the number of oxygen atoms to the number of carbon atoms in theamorphous carbon film. As a result, according to the PET bottle 10obtained by the present example, when the number of carbon atomscontained in the film is 100, the ratio of the number of oxygen atomswas 11 and there were no nitrogen atoms contained.

Next, the oxygen transmission rate of one container per day was measuredas an index of the gas barrier property of the PET bottle 10 obtained bythe present example. The oxygen transmission rate was measured using anoxygen transmission rate measuring device (manufactured by MOCON, USmanufacturer, Trade name: OX-TRAN) at a temperature of 22° C. andhumidity of 60% RH.

As a beverage container, the gas barrier property of the PET bottle 10should preferably be 0.02 ml/day per bottle or less by oxygentransmission rate, and more preferably, 0.015 ml/day or less. If theoxygen transmission rate per bottle exceeds 0.02 ml/day, thetransmission of oxygen may have an adverse effect on the containedobject. According to the PET bottle 10 obtained by the presentembodiment, the oxygen transmission rate per bottle was 0.003 ml/day.

Next, the degree of coloring caused by the amorphous carbon film of thePET bottle 10 obtained by the present example was evaluated bytransmitting light perpendicularly with respect to the side wall of thePET bottle 10 using a color-difference meter to measure the b* value,which is compared with the b* value of the PET bottle 10 before formingthe film, so as to compute the Δb* value as the difference between thetwo values.

The Δb* value should preferably fall within the range of 2 to 7. If theΔb* value is less than 2, the thickness of the amorphous carbon film istoo thin to achieve sufficient gas barrier properties, and if the Δb*value exceeds 7, coloring by the film becomes notable. According to thePET bottle 10 obtained by the present example, the Δb* value was 3.

Next, the PET bottles 10 having the amorphous carbon film coated thereonwere filled with tea beverage, carbonated beverage and beer, which waskept at room temperature for six months, and then subjected toevaluation of content keeping quality. The result is shown in Table 1,together with the aforementioned film thickness, composition, oxygentransmission rate and Δb* value of the film.

Further, as a reference example, a conventional PET bottle 10 having noamorphous carbon film coated thereon was subjected to evaluation ofoxygen transmission rate and content keeping quality under the sameconditions as the present example. The results are also shown in Table1.

Next, the PET bottle 10 having the amorphous carbon film coated thereonwas crushed and formed into chips using an extruder to createregenerated polyethylene terephthalate. The chips of the regeneratedpolyethylene terephthalate resin had very subtle coloring, and can beused to manufacture polyester fibers without any technical problem. As aresult, the above chip was confirmed to have an equivalent recyclingefficiency as the regenerated polyethylene terephthalate resin formed bycrushing the recovered PET bottle 10 of the prior art with no filmcoated thereon and chipped using an extruder.

EXAMPLE 2

According to the present example, a 350 ml PET bottle 10 having anamorphous carbon film with a thickness of 0.04 μm (400 angstrom) coatedon the inner surface was formed under exactly the same conditions asexample 1, except that a mixed gas containing acetylene gas as materialgas and air was fed into the PET bottle 10 as gas components. The mixedgas was supplied by feeding the material gas into the PET bottle 10 at aflow rate of 0.4 sccm/cm² with respect to the inner surface area of thePET bottle 10, and feeding air together with the material gas at a flowrate of 0.035 sccm/cm².

At this time, since the ratio of nitrogen to oxygen in the aircomposition nearly equals 8:2, the oxygen gas in the mixed gascorresponds to 1.6% by volume to the total amount of gas components fedinto the PET bottle 10, and the total amount of nitrogen gas and oxygengas corresponds to 8% by volume thereof.

Next, the ratio of the number of nitrogen atoms or the number of oxygenatoms to the number of carbon atoms in the amorphous carbon film and theoxygen transmission rate per bottle as an index of gas barrier propertywere measured for the PET bottle 10 obtained by the present example in amanner identical to example 1. Further, the degree of coloring caused bythe film and the content keeping quality were evaluated in the manneridentical to example 1. The results are shown in Table 1.

EXAMPLE 3

According to the present example, a 350 ml PET bottle 10 having anamorphous carbon film with a thickness of 0.04 μm (400 angstrom) coatedon the inner surface was formed under the exact same conditions asexample 1, except that a mixed gas containing acetylene gas as materialgas and oxygen gas was fed into the PET bottle 10 as gas components. Themixed gas was supplied by feeding the material gas into the PET bottle10 at a flow rate of 0.4 sccm/cm² with respect to the inner surface areaof the PET bottle 10, and feeding oxygen gas together with the materialgas at a flow rate of 0.032 sccm/cm².

At this time, the oxygen gas corresponds to 7% by volume of the totalamount of gas components fed into the PET bottle 10.

Next, the ratio of the number of nitrogen atoms or the number of oxygenatoms to the number of carbon atoms in the amorphous carbon film and theoxygen transmission rate per bottle as an index of gas barrier propertywere measured for the PET bottle 10 obtained by the present example in amanner identical to example 1. Further, the degree of coloring caused bythe film and the content keeping quality were evaluated in the manneridentical to example 1. The results are shown in Table 1.

EXAMPLE 4

According to the present example, a 350 ml PET bottle 10 having anamorphous carbon film with a thickness of 0.04 μm (400 angstrom) coatedon the inner surface was formed under the exact same conditions asexample 1, except that a mixed gas containing acetylene gas as materialgas and nitrogen gas was fed into the PET bottle 10 as gas components.The mixed gas was supplied by feeding the material gas into the PETbottle 10 at a flow rate of 0.4 sccm/cm² with respect to the innersurface area of the PET bottle 10, and feeding nitrogen gas togetherwith the material gas at a flow rate of 0.096 sccm/cm².

At this time, the nitrogen gas corresponds to 19% by volume of the totalamount of gas components fed into the PET bottle 10.

Next, the ratio of the number of nitrogen atoms or the number of oxygenatoms to the number of carbon atoms in the amorphous carbon film and theoxygen transmission rate per bottle as an index of gas barrier propertywere measured for the PET bottle 10 obtained by the present example in amanner identical to example 1. Further, the degree of coloring caused bythe film and the content keeping quality were evaluated in the manneridentical to example 1. The results are shown in Table 1.

EXAMPLE 5

According to the present example, a 350 ml PET bottle 10 having anamorphous carbon film with a thickness of 0.04 μm (400 angstrom) coatedon the inner surface was formed under the exact same conditions asexample 1, except that a mixed gas containing acetylene gas as materialgas and air was fed into the PET bottle 10 as gas components. The mixedgas was supplied by feeding the material gas into the PET bottle 10 at aflow rate of 0.4 sccm/cm² with respect to the inner surface area of thePET bottle 10, and feeding air together with the material gas at a flowrate of 0.048 sccm/cm².

At this time, since the ratio of nitrogen to oxygen in the aircomposition nearly equals 8:2, the oxygen gas in the mixed gascorresponds to 2.2% by volume of the total amount of gas components fedinto the PET bottle 10, and the total of nitrogen gas and oxygen gascorresponds to 11% by volume thereof.

Next, the ratio of the number of nitrogen atoms or the number of oxygenatoms to the number of carbon atoms in the amorphous carbon film and theoxygen transmission rate per bottle as an index of gas barrier propertywere measured for the PET bottle 10 obtained by the present example in amanner identical to example 1. Further, the degree of coloring caused bythe film and the content keeping quality were evaluated in the manneridentical to example 1. The results are shown in Table 1.

Comparative Example 1

According to the present comparative example, a 350 ml PET bottle 10having an amorphous carbon film with a thickness of 0.04 μm (400angstrom) coated on the inner surface was formed under the exact sameconditions as example 1, except that a mixed gas containing acetylenegas as material gas and oxygen gas was fed into the PET bottle 10 as gascomponents. The mixed gas was supplied by feeding the material gas intothe PET bottle 10 at a flow rate of 0.4 sccm/cm² with respect to theinner surface area of the PET bottle 10, and feeding oxygen gas togetherwith the material gas at a flow rate of 0.052 sccm/cm².

At this time, the oxygen gas corresponds to 12% by volume of the totalamount of gas components fed into the PET bottle 10.

Next, the ratio of the number of nitrogen atoms or the number of oxygenatoms to the number of carbon atoms in the amorphous carbon film and theoxygen transmission rate per bottle as an index of gas barrier propertywere measured for the PET bottle 10 obtained by the present comparativeexample in a manner identical to example 1. Further, the degree ofcoloring caused by the film and the content keeping quality wereevaluated in the manner identical to example 1. The results are shown inTable 1.

Comparative Example 2

According to the present comparative example, a 350 ml PET bottle 10having an amorphous carbon film with a thickness of 0.04 μm (400angstrom) coated on the inner surface was formed under the exact sameconditions as example 1, except that a mixed gas containing acetylenegas as material gas and nitrogen gas was fed into the PET bottle 10 asgas components. The mixed gas was supplied by feeding the material gasinto the PET bottle 10 at a flow rate of 0.4 sccm/cm² with respect tothe inner surface area of the PET bottle 10, and feeding nitrogen gastogether with the material gas at a flow rate of 0.13 sccm/cm².

At this time, the nitrogen gas corresponds to 24% by volume of the totalamount of gas components fed into the PET bottle 10.

Next, the ratio of the number of nitrogen atoms or the number of oxygenatoms to the number of carbon atoms in the amorphous carbon film and theoxygen transmission rate per bottle as an index of gas barrier propertywere measured for the PET bottle 10 obtained by the present comparativeexample in a manner identical to example 1. Further, the degree ofcoloring caused by the film and the content keeping quality wereevaluated in the manner identical to example 1. The results are shown inTable 1.

Comparative Example 3

According to the present comparative example, a 350 ml PET bottle 10having an amorphous carbon film with a thickness of 0.04 μm (400angstrom) coated on the inner surface was formed under the exact sameconditions as example 1, except that a mixed gas containing acetylenegas as material gas and air was fed into the PET bottle 10 as gascomponents. The mixed gas was supplied by feeding the material gas intothe PET bottle 10 at a flow rate of 0.4 sccm/cm² with respect to theinner surface area of the PET bottle 10, and feeding air together withthe material gas at a flow rate of 0.096 sccm/cm².

At this time, since the ratio of nitrogen to oxygen in the aircomposition nearly equals 8:2, the oxygen gas in the mixed gascorresponds to 3.8% by volume of the total amount of gas components fedinto the PET bottle 10, and the total of nitrogen gas and oxygen gascorresponds to 19% by volume thereof.

Next, the ratio of the number of nitrogen atoms or the number of oxygenatoms to the number of carbon atoms in the amorphous carbon film and theoxygen transmission rate per bottle as an index of gas barrier propertywere measured for the PET bottle 10 obtained by the present example in amanner identical to example 1. Further, the degree of coloring caused bythe film and the content keeping quality were evaluated in the manneridentical to example 1. The results are shown in Table 1. TABLE 1Comparative Ref Example Example Ex. 1 2 3 4 5 1 2 3 Material Acetylene —0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 Gas (sccm/cm²) Flow Air — 0 0.035 0 00.048 0 0 0.096 Rate (sccm/cm²) Nitrogen — 0 0 0 0.096 0 0 0.13 0(sccm/cm²) Oxygen — 0 0 0.032 0 0 0.052 0 0 (sccm/cm²) Film Thickness(μm) — 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 Ratio of Nitrogen — 0 6 013 7 0 16 13 Number Oxygen — 11 16 17 12 16 24 13 19 Of Atoms Nitrogen +— 11 22 17 25 23 24 29 32 Oxygen Oxygen transmission 0.03 0.003 0.0110.014 0.011 0.013 0.025 0.017 0.022 rate (ml/day) Δb* — 3 3 3 3 3 3 3 3Container Appearance ⊚ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Content Green Tea X ⊚ ⊚ ◯ ⊚ ◯ Δ ΔΔ Keeping beverage Quality Carbonated X ⊚ ⊚ ◯ ⊚ ◯ Δ Δ Δ beverage Beer X⊚ ⊚ ◯ ⊚ ◯ Δ Δ ΔRatio of number of atoms:Ratio of number of atoms of each element when the number of carbon atomscontained in the film is 100 “Nitrogen + Oxygen” shows total number ofnitrogen and oxygen atomsContainer appearance:⊚ clear and colorless◯ clear brown (subtle coloring)Δ clear brown (with coloring)X clear brown (deep coloring) Content keeping qualityGreen tea beverage:⊚ no change in color/flavor◯ change in color/flavor but practically not a problemΔ change in color/flavorX defective color/flavor Carbonated beverage,Beer:⊚ extremely small change in gas volume (8% or less)◯ small change in gas volumeΔ somewhat large change in gas volumeX large change in gas volume (38% or greater)

Based on Table 1, according to the PET bottles 10 of examples 1 through5 wherein the ratio of the number of nitrogen atoms to the number ofcarbon atoms is 15 or less, or the ratio of the number of oxygen atomsto the number of carbon atoms is 20 or less, or the ratio of the totalnumber of nitrogen atoms and oxygen atoms to the number of carbon atomsis 27 or less when the number of carbon atoms contained in the film is100, the oxygen transmission rate per bottle was 0.015 ml/day or less,which clearly has superior gas barrier properties compared to 0.03ml/day of the PET bottle of the reference example having no film coatedthereon.

Further, according to the PET bottle 10 of comparative example 1 whereinthe ratio of the number of oxygen atoms to the number of carbon atomsexceeds 20, or that of comparative example 2 wherein the ratio of thenumber of nitrogen atoms to the number of carbon atoms exceeds 15, orthat of comparative example 3 wherein the ratio of the total number ofnitrogen atoms and oxygen atoms to the number of carbon atoms exceeds 27when the number of carbon atoms contained in the film is 100, the oxygentransmission rate per bottle all exceeded 0.015 ml/day. Accordingly, itis clear that the PET bottles 10 of examples 1 through 5 have better gasbarrier properties than those of comparative examples 1 through 3.

Further, it is clear that the PET bottles 10 of examples 1 through 5have better content keeping qualities than that of the PET bottle of thereference example or those of the PET bottles 10 of comparative examples1 through 3.

EXAMPLE 6

The present example used the plasma CVD apparatus 1 illustrated in FIG.1 to manufacture a 350 ml PET bottle having its inner surface coatedwith amorphous carbon film.

At first, according to the present example, the PET bottle 10 was storedin the processing chamber 4 of the plasma CVD apparatus 1 illustrated inFIG. 1, and the processing chamber 4 was decompressed to reduce thepressure within the PET bottle 10 to a vacuum degree of 10 Pa. Next, amaterial gas composed of acetylene gas was fed into the PET bottle 10 ata flow rate of 0.4 sccm/cm² with respect to the inner surface area ofthe PET bottle 10, and microwaves of 2.45 GHz and 380 W was radiated for0.6 seconds while maintaining the interior of the PET bottle 10 to thevacuum degree of 10 Pa.

As a result, a PET bottle 10 having an amorphous carbon film with athickness of 0.045 μm (450 angstrom) coated on the inner surface wasobtained.

Next, the PET bottle 10 obtained according to the present example wassubjected to measurement for measuring the ratio of the number ofnitrogen atoms or the number of oxygen atoms to the number of carbonatoms in the amorphous carbon film, the oxygen permeability of the filmand the amount of elution of aldehyde. The results are shown in Table 2.

The ratio of the number of nitrogen atoms or the number of oxygen atomsto the number of carbon atoms in the amorphous carbon film was measuredusing an apparatus for electron spectroscopy for chemical analysis(ESCA).

The oxygen permeability of the amorphous carbon film was shown by avalue computed from a measurement of a PET bottle 10 having theamorphous carbon film coating and a measurement of a PET bottle 10having no amorphous carbon film coating using an oxygen permeabilitymeasuring device (manufactured by MOCON, US manufacturer, Trade name:OX-TRAN) at a temperature of 22° C. and humidity of 60% RH. The value ofthe oxygen permeability correlates to the oxygen transmission rate of abottle per day.

The gas barrier property required for the PET bottle 10 to be used as abeverage container is preferably 0.02 ml per bottle per day or less asthe oxygen transmission rate, and more preferably, 0.015 ml or less. Ifthe oxygen transmission rate per bottle exceeds 0.02 ml/day, thetransmission of oxygen may have an adverse effect on the containedobject. The oxygen transmission rate of a bottler per day is shown inTable 2.

Further, the amount of elution of minor components such as oligomer, lowmolecular-weight components, polymerization catalyst or the likecontained in the resin forming the PET bottle 10 manufactured accordingto the present example was measured using aldehyde, which is a lowmolecular component specific to polyester resin, as the index. Theamount of elution of the aldehyde eluted in the PET bottle 10 when anempty PET bottle 10 having no content was sealed and left for a day wasmeasured using a gaschromatograph, and this value was shown as arelative value to the value measured for a PET bottle 10 having noamorphous carbon film coating, when the value for the PET bottle 10having no amorphous carbon film coating is taken as 100.

EXAMPLE 7

According to the present example, a 350 ml PET bottle 10 having anamorphous carbon film with a thickness of 0.045 μm (450 angstrom) coatedon the inner surface was formed under the exact same conditions asexample 6, except that a mixed gas containing acetylene gas as materialgas and a small amount of air was fed into the PET bottle 10 as gascomponents.

Next, the ratio of the number of nitrogen atoms or the number of oxygenatoms to the number of carbon atoms in the amorphous carbon film, theoxygen permeability of the film and the amount of elution of aldehydewere measured for the PET bottle 10 obtained by the present example in amanner identical to example 6. The results are shown in Table 2,together with the oxygen permeability per bottle per day.

EXAMPLE 8

According to the present example, a 350 ml PET bottle 10 having anamorphous carbon film with a thickness of 0.045 μm (450 angstrom) coatedon the inner surface was formed under the exact same conditions asexample 6, except that a mixed gas containing acetylene gas as materialgas and a small amount of oxygen gas was used.

Next, the ratio of the number of nitrogen atoms or the number of oxygenatoms to the number of carbon atoms in the amorphous carbon film, theoxygen permeability of the film and the amount of elution of aldehydewere measured for the PET bottle 10 obtained by the present example in amanner identical to example 6. The results are shown in Table 2,together with the oxygen transmission rate per bottle per day.

EXAMPLE 9

According to the present example, a 350 ml PET bottle 10 having anamorphous carbon film with a thickness of 0.045 μm (450 angstrom) coatedon the inner surface was formed under the exact same conditions asexample 6, except that a mixed gas containing acetylene gas as materialgas and a small amount of nitrogen gas was used.

Next, the ratio of the number of nitrogen atoms or the number of oxygenatoms to the number of carbon atoms in the amorphous carbon film, theoxygen permeability of the film and the amount of elution of aldehydewere measured for the PET bottle 10 obtained by the present example in amanner identical to example 6. The results are shown in Table 2,together with the oxygen transmission rate per bottle per day.

EXAMPLE 10

According to the present example, a 350 ml PET bottle 10 having anamorphous carbon film with a thickness of 0.045 μm (450 angstrom) coatedon the inner surface was formed under the exact same conditions asexample 6, except that the composition ratio of the mixed gas containingacetylene gas as material gas and a small amount of air was changed.

Next, the ratio of the number of nitrogen atoms or the number of oxygenatoms to the number of carbon atoms in the amorphous carbon film, theoxygen permeability of the film and the amount of elution of aldehydewere measured for the PET bottle 10 obtained by the present example in amanner identical to example 1. The results are shown in Table 2,together with the oxygen transmission rate per bottle per day.

EXAMPLE 11

According to the present example, a 350 ml PET bottle 10 having anamorphous carbon film with a thickness of 0.02 μm (200 angstrom) coatedon the inner surface was formed under the exact same conditions asexample 6, except that the flow rate of material gas containingacetylene gas was suppressed to a low value compared to that of example6.

Next, the ratio of the number of nitrogen atoms or the number of oxygenatoms to the number of carbon atoms in the amorphous carbon film, theoxygen permeability of the film and the amount of elution of aldehydewere measured for the PET bottle 10 obtained by the present example in amanner identical to example 6. The results are shown in Table 2,together with the oxygen transmission rate per bottle per day.

EXAMPLE 12

According to the present example, a 350 ml PET bottle 10 having anamorphous carbon film with a thickness of 0.012 μm (120 angstrom) coatedon the inner surface was formed under the exact same conditions asexample 6, except that the flow rate of material gas containingacetylene gas was suppressed to a low value compared to that of example6.

Next, the ratio of the number of nitrogen atoms or the number of oxygenatoms to the number of carbon atoms in the amorphous carbon film, theoxygen permeability of the film and the amount of elution of aldehydewere measured for the PET bottle 10 obtained by the present example in amanner identical to example 6. The results are shown in Table 2,together with the oxygen transmission rate per bottle per day.

EXAMPLE 13

According to the present example, a 350 ml PET bottle 10 having anamorphous carbon film with a thickness of 0.01 μm (100 angstrom) coatedon the inner surface was formed under the exact same conditions asexample 6, except that the flow rate of material gas containingacetylene gas was suppressed to a low value compared to that of example6.

Next, the ratio of the number of nitrogen atoms or the number of oxygenatoms to the number of carbon atoms in the amorphous carbon film, theoxygen permeability of the film and the amount of elution of aldehydewere measured for the PET bottle 10 obtained by the present example in amanner identical to example 6. The results are shown in Table 2,together with the oxygen transmission rate per bottle per day.

EXAMPLE 14

According to the present example, a 350 ml PET bottle 10 having anamorphous carbon film with a thickness of 0.02 μm (200 angstrom) coatedon the inner surface was formed under the exact same conditions asexample 10, except that a small amount of air was added to the materialgas containing acetylene, and that the flow rate thereof was reduced.

Next, the ratio of the number of nitrogen atoms or the number of oxygenatoms to the number of carbon atoms in the amorphous carbon film, theoxygen permeability of the film and the amount of elution of aldehydewere measured for the PET bottle 10 obtained by the present example in amanner identical to example 6. The results are shown in Table 2,together with the oxygen transmission rate per bottle per day.

Comparative Example 4

According to the present comparative example, a 350 ml PET bottle 10having an amorphous carbon film with a thickness of 0.006 μm (60angstrom) coated on the inner surface was formed under the exact sameconditions as example 6, except that the flow rate of material gascontaining acetylene gas was suppressed to a low value compared to thatof example 6.

Next, the ratio of the number of nitrogen atoms or the number of oxygenatoms to the number of carbon atoms in the amorphous carbon film, theoxygen permeability of the film and the amount of elution of aldehydewere measured for the PET bottle 10 obtained by the present example in amanner identical to example 6. The results are shown in Table 2,together with the oxygen transmission rate per bottle per day.

Comparative Example 5

According to the present comparative example, a 350 ml PET bottle 10having no amorphous carbon film coated thereon was subjected tomeasurement of the amount of elution of aldehyde under the exact sameconditions as example 6. The results are shown in Table 2, together withthe oxygen transmission rate per bottle per day.

Comparative Example 6

According to the present comparative example, a 350 ml PET bottle 10having an amorphous carbon film with a thickness of 0.045 μm (450angstrom) coated on the inner surface was formed under the exact sameconditions as example 6, except that a mixed gas containing acetylenegas as material gas and a small amount of oxygen gas was used.

Next, the ratio of the number of nitrogen atoms or the number of oxygenatoms to the number of carbon atoms in the amorphous carbon film, theoxygen permeability of the film and the amount of elution of aldehydewere measured for the PET bottle 10 obtained by the present example in amanner identical to example 6. The results are shown in Table 2,together with the oxygen transmission rate per bottle per day. TABLE 2Examples Comparative examples 6 7 8 9 10 11 12 13 14 4 5 6 RatioNitrogen 0 6 0 13 7 0 0 0 7 0 — 0 of Oxygen 11 16 17 12 16 11 11 11 1611 — 24 number Nitrogen + 11 22 17 25 23 11 11 11 23 11 — 24 of Oxygenatoms Film thickness 0.045 0.045 0.045 0.045 0.045 0.02 0.012 0.01 0.020.006 — 0.045 (μm) Oxygen 1.0 × 5.27 × 7.93 × 5.27 × 6.96 × 5.15 × 11.8× 15.7 × 18.2 × 27.3 × — 45.5 × permeability 10⁻⁵ 10⁻⁵ 10⁻⁵ 10⁻⁵ 10⁻⁵10⁻⁵ 10⁻⁵ 10⁻⁵ 10⁻⁵ 10⁻⁵ 10⁻⁵ (ml/day/cm²) Oxygen 0.003 0.011 0.0140.011 0.013 0.011 0.017 0.019 0.020 0.024 0.03 0.025 transmission rate(ml/day) Elution of minor <3 6 7 6 7 6 30 38 40 65 100 70 componentsRatio of number of atoms:Ratio of number of atoms of each element when the number of carbon atomscontained in the film is 100 “Nitrogen + Oxygen” shows total number ofnitrogen and oxygen atomsElution of minor components:Relative value to a bottle having no amorphous carbon film coatedthereon, when the value of the bottle having no amorphous carbon film is100

As shown in Table 2, the PET bottles 10 of examples 6 through 14 allhave an amorphous carbon film whose oxygen permeability is 20×10⁻⁵ml/day/cm² or less and have an oxygen transmission rate per bottle perday of 0.02 ml or less, so it is clear that they have superior gasbarrier properties.

Furthermore, the PET bottles 10 of examples 6 through 14 all measured anamount of elusion of minor components taking aldehyde as index that is50% or lower to that of the PET bottle 10 of comparative example 5having no amorphous carbon coating, so it is clear that they havesuperior properties to suppress elution of minor components.

The PET bottles 10 of comparative examples 1 and 3 all have an oxygenpermeability greater than 20×10⁻⁵ ml/day/cm² with respect to theabove-mentioned examples 6 through 14, so it is clear that they do nothave sufficient properties to suppress elution of minor components.

Next, the PET bottles 10 according to examples 6 through 14 were filledwith tea beverage, which were kept at room temperature for six months,and then subjected to content evaluation. As a result, there were verylittle change in color of the contents, and no change in flavor.

Further, the PET bottles 10 of examples 6 through 14 were filled withcarbonated beverage, which were kept at room temperature for six months,and then subjected to content evaluation. As a result, there were verylittle change in gas volume, and the result was good.

Next, the PET bottles 10 of examples 6 through 14 were each crushed toform regenerated polyethylene terephthalate resin chips using anextruding machine, which showed very little coloring. Thereafter, thechips were used to manufacture polyester fibers, which were fabricatedwithout any practical problems. Accordingly, it is clear that the PETbottles 10 of examples 6 through 14 each have equivalent reusability asthe PET bottle having no amorphous carbon film coated thereon.

Industrial Applicability

The plastic container with a coated inner surface and the method formanufacturing the same according to the present invention can be appliedto a container for storing fluid materials such as beverage, food,aerosol or medicine, which can be collected after use and recycled.

1. A plastic container with a coated inner surface having an amorphouscarbon film formed by plasma CVD from a starting material containingcarbon atoms and containing carbon as a main component on the innersurface, wherein when the number of carbon atoms contained in the filmis 100, the amorphous carbon film characterizes in that: a ratio of thenumber of nitrogen atoms to the number of carbon atoms is 15 or less; ora ratio of the number of oxygen atoms to the number of carbon atoms is20 or less; or a ratio of the total number of nitrogen atoms and oxygenatoms to the number of carbon atoms is 27 or less; or the ratio of thenumber of nitrogen atoms to the number of carbon atoms is 15 or less,the ratio of the number of oxygen atoms to the number of carbon atoms is20 or less, and the ratio of the total number of nitrogen atoms andoxygen atoms to the number of carbon atoms is 27 or less.
 2. The plasticcontainer with a coated inner surface according to claim 1, wherein theplastic container is formed of a polyester resin.
 3. The plasticcontainer with a coated inner surface according to claim 1, wherein theplastic container is formed of a polyolefin resin.
 4. The plasticcontainer with a coated inner surface according to claims 2 or 3,wherein the amorphous carbon film has a thickness within the range of0.02 through 0.08 μm.
 5. The plastic container with a coated innersurface according to claim 1, wherein the amorphous carbon film has anoxygen permeability of 20×10⁻⁵ ml/day/cm² or less.
 6. The plasticcontainer with a coated inner surface according to claim 5, wherein theamorphous carbon film has a thickness within the range of 0.007 through0.08 μm.
 7. The plastic container with a coated inner surface accordingto claim 5, wherein the plastic container is formed of a polyesterresin, and has a body portion having a thickness within the range of 0.2through 0.5 mm.
 8. The plastic container with a coated inner surfaceaccording to any one of claims 5 through 7, wherein the plasticcontainer has an inner volume of 2000 ml or less.
 9. The plasticcontainer with a coated inner surface according to claim 1, wherein thestarting material contains acetylene as a main component.
 10. A methodfor manufacturing a plastic container with a coated inner surfacecomprising the steps of placing the plastic container in a plasma CVDapparatus, maintaining an interior of the plasma CVD apparatus to apredetermined vacuum degree, feeding a gaseous starting materialincluding carbon atoms into the plastic container, supplying apredetermined energy into the plasma CVD apparatus to generate plasmawithin the plastic container thereby forming an amorphous carbon filmcontaining carbon as a main component on the inner surface of theplastic container, wherein gas components containing the startingmaterial fed into the plastic container comprises: a nitrogen gas whoseamount being mixed is 20% by volume or less to the total amount of thegas components; or an oxygen gas whose amount being mixed is 10% byvolume or less to the total amount of the gas components; or an oxygengas whose amount being mixed is 10% by volume or less to the totalamount of the gas components, and the total amount of nitrogen gas andoxygen gas being mixed is 15% by volume or less.
 11. The method formanufacturing a plastic container with a coated inner surface accordingto claim 10, comprising the steps of detecting an emission intensity ofplasma of nitrogen based on an emission spectrum of the plasma generatedby the gas components containing the starting material being fed intothe plastic container, and controlling a concentration of a nitrogencontaining compound being mixed into the gas components.
 12. The methodfor manufacturing a plastic container with a coated inner surfaceaccording to claim 10, comprising the steps of detecting an emissionintensity of plasma of nitrogen based on an emission spectrum of theplasma generated from the gas components containing the startingmaterial being fed into the plastic container, and controlling an amountof air being mixed into the gas components.
 13. The method formanufacturing a plastic container with a coated inner surface accordingto claims 11 or 12, wherein when the emission intensity of plasma ofnitrogen exceeds a predetermined intensity, the plastic container havingthe amorphous carbon film coated thereon is eliminated from themanufacturing process.
 14. The method for manufacturing a plasticcontainer with a coated inner surface according to claim 11, wherein thedetection of emission intensity of plasma of nitrogen is carried out byselectively detecting the emission of a specific wavelength range in theemission spectrum.
 15. The method for manufacturing a plastic containerwith a coated inner surface according to claim 10, wherein the plasticcontainer with the coated inner surface is formed of a polyester resin.16. The method for manufacturing a plastic container with a coated innersurface according to claim 10, wherein the plastic container with thecoated inner surface is formed of a polyolefin resin.
 17. The method formanufacturing a plastic container with a coated inner surface accordingto claim 10, wherein the film has a thickness within the range of 0.02through 0.08 μm.
 18. The method for manufacturing a plastic containerwith a coated inner surface according to claim 10, wherein the startingmaterial is substantially composed of acetylene.
 19. The method formanufacturing a plastic container with a coated inner surface accordingto claim 10, comprising the steps of: decompressing the plasma CVDapparatus and maintaining the interior of the plastic container placedin the apparatus to a vacuum degree of 1 through 50 Pa; feeding thestarting material in a form of gas containing the carbon atoms into theplastic container within the range of 0.1 through 0.8 sccm/cm² withrespect to an inner surface area of the plastic container; radiatingmicrowaves with energy within the range of 150 through 600 W into theplasma CVD apparatus; and generating plasma in the plastic container fora period of time within the range of 0.2 through 2.0 seconds, therebyforming the amorphous carbon film on the inner surface of the plasticcontainer.
 20. The method for manufacturing a plastic container with acoated inner surface according to claim 19, wherein if the plasticcontainer with the coated inner surface is a container having noself-shape holding property, the interior of the container placed in theplasma CVD apparatus is maintained at higher pressure than the exteriorthereof.